1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly to a method for fabricating a capacitor of a semiconductor device with greater capacitance by depositing a dielectric layer with a dielectric material, Ta.sub.2 O.sub.5 --Al.sub.2 O.sub.3 with higher structural stability and dielectric constant than a Ta.sub.2 O.sub.5 layer, wherein the Ta.sub.2 O.sub.5 --Al.sub.2 O.sub.3 layer is obtained by adding an aluminum containing compound in the process of depositing a conventional dielectric Ta.sub.2 O.sub.5 layer.
2. Description of the Prior Art
FIG. 1 is a cross-sectional view for illustrating an embodiment of a semiconductor capacitor with a Ta.sub.2 O.sub.5 layer as a dielectric layer in accordance with the prior art.
As shown in FIG. 1, a conventional method for fabricating the Ta.sub.2 O.sub.5 capacitor to be used for a semiconductor DRAM device will be described below.
First of all, doped polysilicon is used for forming a bottom electrode 5, a storage node on a semiconductor substrate, and a Ta.sub.2 O.sub.5 layer 9 is deposited as a dielectric layer on the polysilicon layer 5 by a plasma enhanced chemical vapor deposition (PECVD) method or low pressure CVD (LPCVD) method. In addition, a top electrode (plate electrode) 11, 13 is deposited with TiN and/or polysilicon, thereby forming a capacitor for a DRAM device.
However, for the process of depositing a dielectric layer, a PECVD method of forming a high quality dielectric layer, and a LPCVD method of forming a dielectric layer with low quality but high step coverage, have been mainly applied for depositing the Ta.sub.2 O.sub.5 layer.
Since the Ta.sub.2 O.sub.5 layer 9 generally has an unstable stoichiometry, some substitution type Ta vacancy atoms inevitably remain in the dielectric layer due to a difference in the composition ratio of Ta and O. Furthermore, in the process of forming the Ta.sub.2 O.sub.5 dielectric layer, an organic material of Ta(OC.sub.2 H.sub.5).sub.5, a precursor of Ta.sub.2 O.sub.5, and O.sub.2 (or N.sub.2 O) gas are reacted to release and co-exist carbon atoms (C), hydrocarbon (CH.sub.4, C2H4 etc.) and water (H.sub.2 O)
On the other hand, FIG. 2 is a schematic view for illustrating internal chemical composition and properties of the Ta.sub.2 O.sub.5 layer shown in FIG. 1.
As the Ta.sub.2 O.sub.5 layer 9 is shown in the drawing, due to unstable stoichiometry, it remains in a state of Ta.sub.x O.sub.y, releasing some substitution type Ta vacancy atoms caused by difference in the composition ratio of Ta and O. Furthermore, an organic material of Ta(OC.sub.2 H.sub.5).sub.5, a precursor of Ta.sub.2 O.sub.5, and O.sub.2 (or N.sub.2 O) gas are reacted to release and co-exist carbon atoms (C), hydrocarbon (CH.sub.4, C2H4 etc.) and water (H.sub.2 O) as well.
Therefore, there is a problem in the conventional Ta.sub.2 O.sub.5 capacitor in that the conventional Ta.sub.2 O.sub.5 capacitor increases current leakage and deteriorates dielectric characteristic due to impurities like carbon atoms, ions, radicals remaining in the Ta.sub.2 O.sub.5 dielectric layer, thereby putting a great limitation in application of the Ta.sub.2 O.sub.5 capacitor for a mass production of DRAM devices.